When you think
of audio control
rooms you
most likely recall a glossy
magazine cover shot of a
gigantic room inhabited
by a large mixing desk
with odd-looking geometric
shapes and acoustic treatment of the
walls. Some of those same people would
probably be surprised to discover that, in
television at least, this type of room is the
exception rather than the norm.

Shrinking budgets and the desire to create
content for new markets means that
audio control room budgets continue to
decrease and they’re being forced into ever-
smaller and less functional spaces.

The point of building an audio mix room
in the first place is to give the audio mix
engineer the ability to hear everything with
clarity and accuracy and to do so without
inconveniencing the rest of the crew. Video
editors and graphic artists won’t easily
give up color-matched monitors and light-controlled,
low-glare workspaces, yet audio
mixers are rarely offered quiet, acoustically-true
workspaces to work in.

Part of the problem is that nonlinear
editing software and video production
tools have dropped in price dramatically
as have the machines they run on and the
monitors they use for display. Meanwhile
the cost of audio consoles has remained
high, space is difficult to obtain, and construction
costs are always increasing, all
of which means that audio production
rooms now often cost more than video
production rooms.

In a business that rarely considers audio
anything other than a nuisance, this is
a dangerous position to be in. Of course
there are solid scientific reasons for traditional
audio control room design, so let’s
look at the benefits of large control rooms
and what we can do to minimize the inherent
shortcomings of small control rooms.

LARGER CONTROL ROOMS
SOUND BETTER
One fact that is rarely mentioned when
space is parceled out for audio control
rooms is that low-frequency waveforms
are enormous and they cause enormous
problems in small rooms. If we generate a
20 Hz sine wave and play it through speakers
capable of reproducing it, the resulting
waveform will be 56.5 feet long (68 degree
air at 1,130 feet per second), though most
people will feel this frequency rather than
hear it.

If instead we generate an easily heard 60
Hz sine wave, the resulting wavelength is
18.84 feet long. Low frequencies are omnidirectional,
so they’re essentially emanating
from the speakers in all directions, which
means we end up with some fairly large
waveforms heading for the walls, ceiling
and floor.

As these waveforms are made up of energy,
the room needs to be large enough
to accommodate them or this energy
will build up and create standing waves
(resonant modes). Waveforms created by
mixing sounds together are much more
complex than simple sine waves, so most
small rooms contain multiple problematic
modes. Often these modes result in low-frequency
build-up in the corners and rear
of the control room where the client sits.

Side absorbers

It’s worth noting that even large rooms
have modes, but because there is more
space (volume) the modes will be more
evenly distributed. Smaller rooms mean
less space, so the modes are far more likely
to either interact or separate, which will
cause the frequency response to vary at
different locations throughout the room.
Small, cube-shaped rooms have the most
mode problems of all and should be avoided
at all costs.

The best help for standing waves is
to make the room larger, but since this
is usually not an option such spaces will
need to be treated by using a spectrum
analyzer to locate frequency build-up
where it occurs in the room and then by
careful placement of absorbers and bass
traps to minimize the problem modes as
much as possible.

LARGE ROOMS MINIMIZE
REFLECTIONS
When we sit at the mix position we anticipate
that all sound will emanate directly
from the speakers even though some of
it will be indirect sound reflected from a
surface in the room. Hard surfaces of all
types cause reflections, including the mixing
desk, walls, floors, ceilings and video
monitors.

Reflections are actually normal and help
us determine room dimensions as we listen,
but when these reflections arrive at
the mix position at a decibel level similar
to that of the mix they begin to interfere
with our ability to accurately discern the sound coming from the speakers.

All sounds arriving within the first 50 ms
are interpreted by our brains as if they originated
from the same sound source (Haas
effect). So if there are lots of early reflections
in the soundfield it is unlikely we will
hear them or have any idea that the room
has become part of the mix.

Diffusors in the ceiling

Larger rooms minimize reflections
from walls and ceilings because the distance
from the speakers and the mix position
is greater. In smaller rooms those
surfaces are much closer. Reflections
from them must be factored in and dealt
with. Large rooms also give midrange and
high frequencies more time to abate in
air, yet those same frequencies are likely
to encounter a wall or some other surface
in a small room before they have the
chance to dissipate, so they become audible
reflections.

Whether a reflection is early, late or
somewhere in between, it is advantageous
to minimize it to the point that it does
not interfere with the mix engineer’s ability
to accurately hear at the mix position.
This can be done by moving or removing
the reflective surfaces, placing absorption
where the reflections occur or adding a diffusor
to scatter them and minimize their
impact. Usually a combination of the three
provides the best solution and care must be
taken to avoid adding so much absorption
that the room becomes lifeless and fatiguing
to mix in.

We’ve looked at only a couple of aspects
of control room acoustic issues in this column
and just at a very high level. The science
of acoustics is much deeper, even on
these two aspects, than we have the space
to delve into here. If you find yourself in
need of help with room acoustic issues, hiring
a professional acoustic consultant will
be money well spent.

Next time we’ll look at isolation, room
shapes, some practical applications and
continue assessing how to do the best
work we can in small control room spaces.

Jay Yeary is not an acoustician,
but is fortunate enough to know and
work alongside people who have considerable
talent when it comes to audio
room acoustics. He can be reached
through TV Technology or via Twitter at
@TVTechJay.

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